This invention relates to a light-sensitive silver halide color photographic material, more particularly, to a light-sensitive silver halide color photographic material having high sensitivity and excellent color reproducibility.
In the color photography employing a light-sensitive silver halide color photographic material, the color reporoduction is carried out, in general, by the subtractive color process. Namely, in an ordinary light-sensitive silver halide color photographic material, a yellow dye forming coupler is used in a blue light- sensitive emulsion layer, a magenta dye forming coupler in a green light-sensitive emulsion layer, and a cyan dye forming coupler in a red light-sensitive emulsion layer. In the color developing after imagewise exposure, an oxidation product of a color developing agent to be formed by development of light-sensitive silver halides undergoes a coupling reaction with the above dye forming couplers to form yellow, magenta and cyan dye images, respectively, whereby the color reproduction is achieved.
The color reproducibility is one of the most important performances which may decide the quality of a color photograph. Accordingly, since the discovery of the principle of the above color photography, there has been made a number of studies for improvement in the color reproducibility.
Although there are many factors which affect the color reproducibility, important factors among those are the spectral sensitivity characteristics of a light-sensitive silver halide emulsion and the spectral absorption characteristics of a color dye.
In the spectral sensitivity characteristic of a light-sensitive silver halide emulsion, what is particularly questioned is a question of the blue sensitivity of a silver halide having been subjected to spectral sensitization. In nature, the silver halide has the sensitivity only to blue light in a visible light, but it is possible by the technique of spectral sensitization which is known in the art to make the silver halide have the sensitivities to green light and red light and further to infrared light also. Therefore, by the spectral sensitization, silver halide grains are made to have the sensitivities to blue light and light in a spectral sensitized region (for example, green light, red light, etc.). Because of the blue light-sensitivity of the silver halide having been subjected to the spectral sensitization, however, it follows that, in the above-mentioned light-sensitive silver halide color photographic material, magenta and cyan color development may also incidentally take place besides yellow color development, during the course of color developingt after imagewise exposure by blue light, to bring about an undesirability in the color reporoduction. As one of techniques to solve this problem, there is a method in which a yellow filter is provided below the blue light-sensitive emulsion layer, i.e., on the side distant from a light source. This method is greatly effective, but has disadvantages such that it reults in high production cost, has no effect on the layers upper than the yellow fileter (namely, when, for example, a blue light-sensitive emulsion layer or a red light-sensitive emulsion layer is provided on the side nearer to the light source than the blue light-sensitive emulsion layer). In any event, from a viewpoint of the color reproduction, it is preferable to make the sensitivity to the spectral sensitized region as high as possible as compared with the blue light-sensitivity.
Next, as to the spectral absorption characteristics, what are preferable for the color reproduction may be mentioned to be that the wavelength giving maximum spectral absorption in the visible region (hereinafter referred to as "primary absorption") and the shape of a peak of the primary absorption are adequate, and that there is less excessive absorption other than the primary absorption (hereinafter referred to as "secondary absorption"). Firstly, in respect of the primary absorption, it is generally known to be improved to a considerable extent by selecting substituents for a coupler or high boiling organic solvents for a coupler, and there can be said that, in the present state of the art, suitable ones have been selected. However, in respect of the secondary absorption, in particular, the secondary absorption in blue regions of magenta and cyan dyes, which gives seriously bad influence to the color reproducibility, it has been attempted in general in the art to improve it by a masking method using a colored coupler, a method utilizing the interimage effect, etc. However, it does not necessarily follow that these methods can be always used. For instance, the masking method using a colored coupler can be utilized for intermediate images such as those in color negative films, but can not be utilized for what are to become final images such as those in color reversal films, color photographic papers, etc. Accordingly, it has been desired to produce a coupler capable of giving a color dye having less secondary absorption.
In particular, a magenta dye forming coupler of pyrazolone series (hereinafter referred to as "magenta coupler"), generally used in the present art, has particularly a large secondary absorption in a colored dye (a pyrazolone-azomethine dye), and thus its improvement has been strongly desired.
The magenta coupler having less secondary absorption is known to include pyrazolinobenzimidazole series compounds disclosed in German Patents No. 10 70 030 and No. 11 27 220, pyrazolotriazole series compounds disclosed in French Patent No. 2,075,583, U.S. Pat. Nos. 3,705,896 and No. 3,725,067, British Patent No. 1,252,418, etc., and indazolone series compounds disclosed in U.S. Pat. No. 2,673,801, etc.
However, in the above-mentioned compounds, there are many compounds having disadvantages such that the color property is insufficient or that colored dyes are unstable to light or heat, and they have scarcely put into practical use. Among them, the compounds of pyrazolotriazole series are known to have relatively good performance, have less secondary absorption, show sharpnesss in the shape of the primary absorption, and are desirable couplers from the view point of the color reproduction. However, the above pyrazolotriazole series couplers, when they are designed to be put into practical use, were found to have disadvantages such that they are insufficient in the sensitivity and are liable to cause photographic fogs. Therefore, it has become understood that, in order to improve the color reproducibility by using the pyrazolotriazole series magenta couplers, essential techniques are to make high the sensitivity of a silver halide emulsion and to decrease fogs.
A method most well known as the technique to make high the sensitivity is to enlarge the size of light-sensitive silver halide grains. However, according to this method, it follows that not only the sensitivity in the spectral sensitized region of silver halide grains but also the sensitivity to blue light are raised (generally in such a manner that the rise in sensitivity to blue light is larger), and thus such a method is not preferable from the viewpoint of the color reproduction as mentioned above. In order to raise the sensitivity in the spectral sensitized region, it is considered necessary to increase the amount of sensitizing dyes or to select other sensitizing dyes. However, such measures may often give a bad influence to other photographic performances or cause the change in spectral sensitivity, and also, in the present state in the art, considerably desirable sensitizing dyes have been used under desirable conditions. Accordingly, it is difficult to make sensitization in a large region by such measures.
As a countermeasure to the increase in fogs, it is known to use an antifoggant. The antifoggant is known to include, for example, azaindenes, triazoles, tetrazoles, imidazolium salts, etc. However, if these antifoggants are used in a large amount, the lowering of sensitivity will be caused, or even if used in a large amount, it often occurs that the antifogging effect is not sufficient, and thus no fundamental solution will be achieved.
In the techniques mentioned in the foregoing, there has been obtained no light-sensitive silver halide color photographic material having high sensitivity and excellent color reproducibility.